The classification of angiosperm families is based on flower structure, including the number and arrangement of stamens, petals and sepals. For example, the ornamental flower in the above photo belongs to the genus Cistus in the rock-rose family (Cistaceae). This unique family has 5 sepals and 5 petals with numerous stamens. Although it superficially resembles the rose family (Rosaceae), the stamens are attached to the base of the ovary and not on a hypanthium as in the Rosaceae. To test your recognition of plant families, please refer to the following crossword puzzle.

Helianthemum scoparium, another member of the rock-rose family (Cistaceae). This is a small shrub native to the coastal sage scrub and chaparral of San Diego County.

1. Monocot & Dicot Comparison

Classes Monocotyledoneae & Dicotyledoneae

2. Illustration of Bisexual Flower

Bisexual flower showing all 4 characteristic parts which are technically modified leaves: Sepal, petal, stamen & pistil. This flower is referred to as complete (with all 4 parts) and perfect (with "male" stamens and "female" pistil). The ovary ripens into a fruit and the ovules inside develop into seeds. Most flowers contain several to many ovules. Incomplete flowers are lacking one or more of the 4 main parts. Imperfect (unisexual) flowers contain a pistil or stamens, but not both. Species populations with male and female flowers borne on separate male and female individuals are termed dioecious. Species populations with separate male on female flowers borne on the same individuals are termed monoecious.

3. Passionflower: Complex & Unusual Bisexual Flower

A. Corona

B. Anther

C. Style

D. Sepal

E. Petal

The blue-crown passionflower (Passiflora caerulea) on the Palomar College campus. The blossom has five sepals (D), five petals (E), five versatile anthers (B) and three styles (C). Between the base of the petals and the stamens is a conspicuous, fringelike crown or corona (A) composed of numerous linear lobes.

The endemic passionflower (Passiflora foetida var. galapagensis) growing on the Island of Santa Cruz in the Galapagos Archipelago.

One of the most remarkable methods of pollination in angiosperms involves the tiny, boat-like male flowers of ribbon-grass (Vallisneria), a genus of about ten species in the monocotyledonous frog's-bit or waterweed family (Hydrocharitaceae). [Other genera in this family include Elodea, Najas, and the troublesome, perennial aquatic weed Hydrilla verticillata. Vallisneria is an unusual genus of dioecious species that live submersed at the bottom of freshwater ponds. The plants produce clusters (rosettes) of long, ribbon-like leaves that develop from runners rooted in the bottom sediments. Vallisnerias have adapted to an underwater existence, except at the time of flowering. Female plants produce single flowers on long stalks (peduncles) that rise to the surface. Each flower floats horizontally on the water surface, with the receptive stigma exposed to the male flowers. Male plants produce hundreds of flower buds (100-250) within a translucent spathe in the leaf axils near the base. At maturity, the tiny male flower buds are gradually released and rise to the surface where they open as the three sepals fold back into a reflexed position. Each male flower is only about one millimeter in diameter, with one or two erect stamens exposed to the air. The reflexed sepals serve as pontoons, keeping the stamens above the water and the pollen dry. The minute male flowers are pushed across the water surface by the slightest breeze, eventually bumping into the exposed stigma of a female flower resting horizontally on the water surface. This type of contact pollination also occurs in duckweeds (Lemnaceae), where the minute plants are pushed together by the wind. After pollination, the vallisneria ovary develops into a seed-bearing fruit. In some species the flower stalk (peduncle) coils into a spiral and pulls the ripening fruit below the water surface.

A dried male flower from North American ribbon-grass (Vallisneria americana). It was photographed through a compound microscope with substage illumination at 40 X magnification. The entire flower is about one millimeter across. Note the single, erect stamen and three reflexed sepals. Numerous spherical pollen grains are visible around the anther. The sepals serve as pontoons that keep the stamen and pollen above the water surface. Another species (V. spiralis) has two stamens. This specimen courtesy of Francis Underwood.

The ripened ovary (capsule) of an unknown orchid cut lengthwise (longitudinally) into two halves. The capsule is composed of three carpels and contains more than one million minute seeds. The withered flower (perianth) is attached to the top of the ovary, a condition known as epigynous (above gynoecium). Epigynous also refers to flowers with an inferior ovary. The term inferior does not refer to a lesser rank or degree. In fact, flowers with inferior ovaries are considered more advanced on the evolutionary scale, culminating in the orchids. The U.S. penny is shown as a size relationship. It has a diameter of 19 mm and a circumference of 59.7 mm. [One inch = 25.4 millimeters.]

Microscopic view of the seed of a coral-root orchid (Corallorhiza maculata). The individual seed is only about 0.2 mm in diameter. In fact, there are unusual bacterial cells that are larger than this orchid seed. The resolving power for an unaided human eye with 20-20 vision is about 0.1 mm. With its cellular sheath (seed coat) removed, this seed is barely visible to the naked eye. Certain epiphytic orchids of the tropical rain forest produce the world's smallest seeds weighing only about one 35 millionths of an ounce (1/35,000,000) or 0.81 micrograms. Some seeds are only about 1/300th of an inch long (85 micrometers). One seed capsule from a single flower may contain up to four million seeds. They are dispersed into the air like minute dust particles or single-celled spores, eventually coming to rest in the upper canopy of rain forest trees. The seeds of some species are no larger than fungal spores and occur in a loose cellular sheath. Since the seeds have no endosperm and a minute, undifferentiated embryo, there are practically no food reserves. In order to germinate under natural conditions, they must establish a symbiotic relationship with a compatible mycorrhizal soil fungus. During early stages of development, the fungus supplies critical nutrients to the orchid seedling. Later the orchid may become fully independent, or it may retain its mycorrhizal relationship throughout its life. The above coral-root orchid seed (Corallorhiza) grows into a nonphotosynthetic mycotrophic wildflower that is completely dependent on its mycorrhizal fungus. Throughout its life, the orchid absorbs carbohydrates and minerals from its fungal partner, which in turn absorbs these vital nutrients from the roots of nearby forest trees. In a laboratory, orchid seeds can be grown in nutrient agar, like a sterile (axenic) culture of bacteria or fungal spores.

Several remarkable examples of orchid pollination involve the seduction of male wasps and bees by orchid flowers. Flowers of the Australian orchid Cryptostylis leptochila resemble a female ichneumon wasp. The male ichneumon wasp attempts to copulate with the flowers, thus insuring cross pollination as he mounts the blossoms. Other species of Cryptostylis orchids also entice male wasps to visit their blossoms for pseudosexual encounters. Orchids of the genus Ophrys are well-known for their flowers that mimic bees and wasps. The Mediterranean orchid Ophrys fusca seduces a male bee before the female bees have emerged from their pupal cases. The following image shows an uncanny "face" on column of this vanda orchid. Nectar guide lines are visible of the lower "lip" petal (labellum). With some imagination, the flower superficially resembles the head and front legs of an insect. Whether hymenopterans perceive this flower as an insect is pure speculation by this author.

A "lady slipper" orchid of the genus Paphiopedilum. Approximately 50 species of these beautiful orchids are native from the Himalayas to the Philippines and south to New Guinea. Some are pollinated by wasps that are temporarily captured in the bulbous "slipper." The escape route forces them to crawl next to the stamen where they are "dusted" with pollen. These orchids have been extensively hybridized into numerous striking and bizarre forms.

This beautiful orchid native to Madagascar is often called the "Darwin orchid" (Macroplectrum sesquipedale), also known as Angraecum sesquipedale. In fact, to reach the nectar of this orchid requires a 30 centimeter (eleven inch) proboscis to penetrate the long nectar spur (white arrow). Long before it was found in nature, both Charles Darwin and Alfred Wallace (founding fathers of the principles of evolution) predicted that it would be a long-tongued hawk moth.